The little blue pill that has long been known to enable and enhance sexual performance in men could also be used as a treatment for heart disease, according to a new study.

Viagra hit the market in 1998 after the Food and Drug Administration approved its use for the treatment of impotence in men. Over the next decade, it became the most commercially successful drug on the market, with more than 1.8 billion pills used by 35 million people.

Lost in Viagra’s salacious reputation was the fact that the drug (under generic name Sildenafil) was originally designed to treat high blood pressure and cardiovascular disease due to its ability to widen blood vessels and increase blood flow. "Its results as an anti-angina drug were only modest, but patients reported the unexpected side effect of improved erections," explained lead author Andrea M. Isidori on the BioMed Central website. "The focus of interest in this drug shifted rapidly from the heart to the bedroom."

Although Viagra was widely viewed as a successful "love drug," its early history as a viable treatment for heart patients was tainted when a some users suffered cardiovascular events, a few resulting in sudden death. Afterward, most doctors stopped prescribing it to men with heart disease. Later research found that the problems occurred when Viagra was taken in combination with other medications containing nitro compounds — used to regulate various aspects of the nervous, immune, and cardiovascular systems. The drug combo increases the risk of a sudden drop in blood pressure during sex, which could be harmful for someone with existing heart problems. "Clearly, this is the result of a series of conditions occurring simultaneously," said Isidori. "When Viagra is taken correctly, it is no longer a concern."

The new study, which mainly focused on men, could not only change the perception that Viagra is dangerous for people with heart problems, but also show it can help improve heart function. Phosphodiesterase-5 inhibitor (PDE5i) is the main ingredient in Viagra and other drugs commonly used to treat erectile dysfunction. The inhibitor blocks the enzyme PDE5, which prevents relaxation of smooth muscle tissue. To test the effectiveness of PDE5i in safely protecting the heart, the researches analyzed trials involving 1,622 patients who were treated with either PDE5i or a placebo. 

The research revealed that PDE5i prevented the heart from enlarging and changing shape in patients suffering from left ventricular hypertrophy, a condition that causes thickening of the muscles in the left ventricle. PDE5i also improved heart performance in all patients with different heart conditions, with no negative effect on the patients' blood pressure.

The study's authors concluded that PDE5i could be safely administered to men who suffer from heart-muscle thickening and early-stage heart failure. But because most of patients they analyzed were men, the findings call for a larger trial on sex-specific, long-term responses.

"We found that the main ingredient in Viagra can be used as an effective, safe treatment for several patients with heart disease," Isidori said in a press statement. "Large clinical trials are now urgently needed to build on these encouraging findings."

That is exactly what needs to happen, former president of Pfizer Global Research and Development John LaMattinawrote on Forbes.com. But the kind of studies required to further test PDE5i would take years and hundreds of millions of dollars to conduct. LaMattina said he is skeptical that companies such as Pfizer would be willing to take on such an expensive, long-term investment. "Despite the interesting results, it remains to be seen whether a study of sufficient size and robustness necessary for the regulatory approval of a PDE-5 inhibitor for use in heart failure patients will ever be done," he concluded. "It is possible that an entity like the (National Institutes of Health) would take this on. However, in this time of reining in healthcare costs, the potential of PDE-5 inhibitors as drugs for treating heart failure may never be realized."